Prophylaxis of venous thromboembolism in general surgery in Spain. Analysis of a national survey

INTRODUCTION

Venous thromboembolism (VTE) represents a serious postoperative complication that can be prevented by adequate thromboprophylaxis. Surveys provide relevant information about clinician's attitudes and preferences regarding VTE prophylaxis.

METHODS

Transversal, descriptive study based on a survey sent to general surgeons members of the Spanish Association of Surgeons (AEC), that included 31 questions regarding postoperative VTE and its prevention, as well as three clinical scenarios.

RESULTS

530 surgeons, 21.8% of the 2,429 invited by electronic mail to participate, completed the survey. Most of the answering clinicians work on in big teaching hospitals, and 28.5% are residents. VTE represents a serious problem for 28% of participants. Although 81% consider that their knowledge on the prevention of postoperative VTE is adequate, a similar percentage recognizes the need for further education. The vast majority (98.7%) use low molecular weight heparins, which are considered the most effective and safe modality, followed by mechanical methods. The Caprini risk assessment score is used by 81% of surgeons, who usually start pharmacological prophylaxis preoperatively. However, there are remarkable differences in the dosing of heparins, timing of initiation, and duration, especially in non-oncologic surgical patients.

CONCLUSIONS

Most Spanish surgeons are interested in the prevention of postoperative VTE. Overall, the level of knowledge on thromboprophylaxis is adequate. However, our results indicate that there is a need for better education on relevant practical aspects of prophylaxis that could be achieved by incorporating recommendations from recent guidelines to local hospital-based protocols.

Product Individuality of Commercially Available Low-Molecular-Weight Heparins and Their Generic Versions: Therapeutic Implications

The currently available brand-name low-molecular-weight heparins (LMWHs) in the United States include dalteparin (Pfizer), enoxaparin (Aventis), and tinzaparin (Pharmion). Other products available, in Europe, include certoparin (Novartis), reviparin (Abbott), nadroparin (GlaxoSmithkline), and parnaparin (Alpha-Wasserman). Each of these LMWHs has a characteristic molecular weight profile and biological activity in terms of an anti-FXa and anti-FIIa potency. The mean molecular weight of these drugs ranges from 4.0 kDa to 7.0 kDa and the anti-FXa:anti-FIIa ratio ranges from 1.5 to 3.5. These agents may also be characterized by the presence of specific chemical end groups such as 2-O-sulfo-4-enepyranosuronic acid at the nonreducing terminus (enoxaparin) or 2,5-anhydro-D-mannose at the reducing terminus (dalteparin). Further, the component oligosaccharide chains exhibit product-specific distribution profiles. It is now widely accepted that individual LMWHs are chemically unique agents and cannot be interchanged therapeutically. Each commercial LMWH has been individually developed for specific clinical indications, which are dose and product dependent. Recently, several generic LMWHs have become available in India (Cutenox and Markaparin) and South America (dilutol, clenox, dripanina), and three companies have filed for regulatory approval of a generic version of enoxaparin in the United States. As the primary aim of a generic drug is to reduce cost without compromising patient care, a generic drug is required to be chemically and biologically equivalent to the pioneer drug. Because LMWHs represent complex natural mucopolysaccharide drugs that have undergone chemical and enzymatic modifications, physicochemical and biological information in addition to molecular weight and anti-FXa:anti-FIIa ratio should be used to determine generic equivalency to the branded drug. We have utilized a previously reported approach to systematically compare three generic versions of enoxaparin obtained from India and Brazil with the branded enoxaparin (Lovenox) available in the United States. Testing included molecular and structural profiling, evaluation in clot-based and amidolytic anti-FXa and anti-FIIa assays, and heparinase-I digestion profiles. While the molecular profiles (4.8 ± 1.8kD) and anticoagulant potencies as determined by activated partial thromboplastin time (APTT) were comparable for all four agents, the generic products showed variations in the thrombin time (TT) and Heptest assays. Two generic and the branded enoxaparin were readily digested by heparinase-I, losing most of their anticoagulant activity, but one generic product resisted digestion. This may have been due to a unique structural feature in this product. These studies show that, while generic LMWHs may exhibit acceptable molecular weight and anti-FXa profiles, they can exhibit assay-based differences and digestion profiles. Testing in animal models to determine safety, efficacy, and pharmacodynamic parameters may be important to verify equivalence. In order to assure that the generic LMWHs are equivalent to branded LMWHs such that equivalent clinical results are obtained, there is a need to develop clear stepwise guidelines that will establish equivalency in terms of physical, chemical, biochemical, pharmacokinetic, and pharmacodynamic properties for these anticoagulant drugs.

Generic Forms of Low-Molecular-Weight Heparins: Some Practical Considerations

This commentary briefly reviews the controversies of therapeutic and generic interchangeability, as they apply to the antithrombotic drug class called low-molecular-weight heparin (LMWH). Recommendations are prepared for the generic LMWH approval process by various regulatory bodies.

Collaborative study for the establishment of replacement batches of heparin low- molecular-mass for assay biological reference preparations

A collaborative study was run by the European Directorate for the Quality of Medicines & HealthCare (EDQM) in the context of the Biological Standardisation Programme (BSP), under the aegis of the Council of Europe and the European Commission, to establish replacement batches for the dwindling stocks of the Heparin low-molecular-mass for assay European Pharmacopoeia Biological Reference Preparation (BRP). The replacement batches of BRP are intended to be used in the assays for anti-Xa and anti-IIa activities, as described in the European Pharmacopoeia (Ph. Eur.) monograph Heparins, low-molecular-mass (0828). Three freeze-dried candidate batches were calibrated against the current International Standard (IS) for Heparin, lowmolecular- weight (2nd IS, 01/608). For the purpose of the continuity check between subsequent BRP batches, the current Heparin low-molecular-mass for assay BRP (batch 5) was also included in the test panel. Thirteen official medicines control and manufacturers laboratories from European and non-European countries contributed data. A central statistical analysis of the datasets was performed at the EDQM. On the basis of the results, the 3 candidate materials were assigned a potency of 104 IU/vial for the anti-Xa activity and 31 IU/vial for the anti-IIa activity. Taken into account the preliminary stability data and the results of this collaborative study, the 3 batches of candidate BRP were adopted in June 2010 by the Commission of the Ph. Eur. as Heparin low-molecular-mass for assay BRP batches 6, 7 and 8.

Variability of heparins and heterogeneity of low molecular weight heparins

Chemical and physical characteristics, building blocks, constitutive disaccharides, sulfation degree, and biological activities of heparins (UFHs) and of low molecular weight heparins (LMWHs) obtained by different depolymerization processes are examined comparatively in terms of structure characteristics, content of 1,6-anhydro rings, and other fingerprints. The heterogeneity of different LMWHs depends on different manufacturing processes and on particular specifications of pharmacopoeias. The reported examples prove that the variability among samples of LMWHs manufactured by the same process is quite limited. Most of the variability is derived from the parent UFH. In contrast, fingerprint groups and residues are specific to the depolymerization process and their extent can be roughly controlled through the process parameters.

Collaborative study to establish the Low-molecular-mass heparin for assay--European Pharmacopoeia Biological Reference Preparation

Thirty laboratories participated in a collaborative study to calibrate replacements for the 1st International Standard for Low Molecular Weight Heparin and the European Pharmacopoeia Low-molecular-mass heparin for assay Biological Reference Preparation. Two freeze-dried materials and one liquid preparation were included in the study. All three samples gave excellent intra- and inter-laboratory variations (majority of mean % geometric coefficient of variation < 10 %) when assayed against the 1st International Standard by both anti-Xa and anti-IIa assays. There were no major differences found between potency estimates using all methods and that obtained using European Pharmacopoeia method only. Overall, this study showed that the differences between the candidates are marginal. Based on the results of the study Sample B, 01/608 was established as the 2nd International Standard for Low Molecular Weight Heparin. Sample A, 01/592 and sample C, the liquid preparation, were established as replacements for the European Pharmacopoeia 'Low-molecular-mass heparin for assay' Biological Reference Preparation.

Low-molecular-weight heparin as bridging anticoagulation during interruption of warfarin: assessment of a standardized periprocedural anticoagulation regimen

BACKGROUND

The treatment of patients at increased risk for arterial thromboembolism who require temporary interruption of warfarin sodium therapy is a common clinical problem. We investigated the efficacy and safety of a standardized periprocedural anticoagulation regimen with low-molecular-weight heparin.

METHODS

We studied 650 consecutive patients with a mechanical heart valve, chronic atrial fibrillation, or embolic stroke who required interruption of warfarin therapy because of an invasive procedure. Warfarin was stopped 5 or 6 days before the procedure, and patients received subcutaneous dalteparin sodium, 100 IU/kg twice daily, starting 3 days before the procedure. The risk of postprocedural bleeding determined postprocedural anticoagulant management. In patients undergoing a non-high-bleeding-risk procedure who had adequate postprocedural hemostasis, warfarin was resumed on the evening of the procedure, and dalteparin sodium, 100 IU/kg twice daily, was resumed on the next day and continued until the international normalized ratio was 2.0 or more. If postprocedural hemostasis was not secured, the resumption of dalteparin was delayed. In patients undergoing a high-bleeding-risk procedure, warfarin was resumed on the evening of the procedure, but dalteparin was not given after the procedure.

RESULTS

Patients were followed up during the preprocedural and postprocedural period for a mean of 13.8 days (range, 10-18 days). In 542 patients who underwent a non-high-bleeding-risk procedure, there were 2 thromboembolic events (0.4%), 4 major bleeding episodes (0.7%), and 32 episodes of increased wound-related blood loss that precluded postprocedural dalteparin administration (5.9%). In 108 patients who underwent a high-bleeding-risk procedure, there were 2 deaths (1.8%) possibly due to thromboembolism and 2 major bleeding episodes (1.8%).

CONCLUSIONS

In patients at increased risk for arterial thromboembolism who require temporary interruption of warfarin therapy, a standardized periprocedural anticoagulant regimen with low-molecular-weight heparin is associated with a low risk of thromboembolic and major bleeding complications.

Anticoagulation therapy

Despite refinements and standardization in the use of anticoagulants, many problems remain for clinicians. Dr. Crowther describes appropriate starting and maintenance doses of warfarin, factors accounting for inter- and intra-observer variability and importantly, the management of the over-anticoagulated patients and bleeding patients. Dr. White compares unfractionated heparin (UFH) and low molecular weight heparin (LMWH) and addresses whether there truly are differences in the efficacy and safety of different LMWH's for both arterial and venous indications. Dr. Ortel discusses the management of the problem patient who requires anticoagulants, the management of heparin-induced thrombocytopenia, the pregnant patient, the obese patient, patients who have renal insufficiency and/or liver disease, patients with malignant disease, and other challenging patient populations.

Randomized trial of different regimens of heparins and in vivo thrombin generation in acute deep vein thrombosis

Low-molecular-weight and unfractionated heparins are frequently used to treat venous thromboembolism, but it is not known whether they are equally effective in inhibiting in vivo generation of thrombin. In this multicenter trial, 1048 patients were randomized to intravenous unfractionated heparin (group A), twice daily low-molecular-weight heparin (reviparin) for 1 week (group B), or once daily reviparin for 4 weeks (group C). All patients received vitamin K antagonists. Blood samples withdrawn at the baseline and at weeks 1 and 3 were analyzed using markers of in vivo thrombin generation and other coagulation parameters. During the first 3 weeks symptomatic recurrent deep vein thrombosis-pulmonary embolism (DVT/PE) occurred in 17 (4.5%) of 375 patients in group A compared with 4 (1.0%) of 388 patients in group B, and 9 (2.4%) of 374 patients in group C. Forty percent of patients in group A, 53.4% in group B, and 53.5% in group C showed 30% or greater reduction in thrombus size assessed by venography. Patients in group B had significantly greater reduction in D-dimer, prothrombin fragments 1 and 2 (F1 + 2), endogenous thrombin potential (ETP), and thrombin-antithrombin (TAT) complexes compared to groups A and C. Greater release of tissue factor pathway inhibitor (TFPI) and reduction in levels of thrombin activatable fibrinolysis inhibitor (TAFI) and fibrinogen were significantly more pronounced in group C patients. Reviparin administered twice daily plus vitamin K antagonist is more effective in inhibiting in vivo thrombin generation compared to intravenous unfractionated heparin plus vitamin K antagonist, and reviparin once daily produced significantly higher TFPI release and greater reduction in TAFI and fibrinogen levels.

Anticoagulation management of valve replacement patients

Anticoagulation regimens vary according to surgeon, nature of the valve (mechanical or biological), its position and other risk factors for stroke. The American College of Chest Physicians (2001) have made the following recommendations to protect patients with prosthetic heart valves from developing a stroke: (i) For mechanical heart valves: Anticoagulation with Warfarin at an INR range 2-3 for patients with a bileaflet mechanical valve in the aortic position; (ii) in the mitral position, an INR of 2.5-3.5 is recommended; an alternative recommendation is an INR of 2-3 in combination with aspirin (80 mg/day); and (iii) in patients with a mechanical valve and a history of systemic embolization, an INR of 2.5-3.5 combined with low-dose aspirin (80-100 mg) is recommended; when Warfarin therapy is initiated, the doses for patients aged <70 years is 4 mg, and for patients aged >70 years it is 3 mg. While it is important to recognize that the therapeutic range for Warfarin is narrow, recommendations have also been established to manage patients with high INRs and for the temporary discontinuation of anticoagulant therapy when they undergo surgical procedures. Rapid anticoagulation can be achieved either with unfractionated heparin or with low-molecular weight heparin (LMWH). Heparin is initiated with an intravenous bolus of 80 U/kg bodyweight, and an infusion of 18 U/kg/h. The activated thromboplastin time should be 60-80 s. An alternative to intravenous heparin is subcutaneous LMWH, which is prescribed in a mg/kg dose. In the event of valve thrombosis in patients who are hemodynamically unstable, surgical exploration with thrombectomy is indicated, with or without valve replacement. In patients who are hemodynamically stable, thrombolytic therapy is recommended initially.

Cost comparison of tinzaparin versus enoxaparin as deep venous thrombosis prophylaxis in spinal cord injury: preliminary data

Thromboembolic events are major causes of morbidity and mortality in patients with spinal cord injuries. Low molecular weight heparins are recommended as prophylaxis against such events. The purpose of the current study was to perform a cost analysis of tinzaparin versus enoxaparin using published efficacy and safety data as deep vein thrombosis and pulmonary embolism prophylaxis in this population. All published English language articles evaluating either tinzaparin or enoxaparin as pharmacoprophylaxis in spinal cord-injured patients were identified. Data from these studies were subjected to cost-effectiveness analyses followed by sensitivity analyses to determine which agent is the most cost-effective in these patients. Results demonstrated that tinzaparin 3500 U daily and enoxaparin 30 mg every 12 h are both cost-effective agents for thromboembolism prophylaxis in patients with spinal cord injuries.

The outcome of ambulatory DVT management using a multidisciplinary approach

Low molecular weight heparins (LMWHs) have been demonstrated to be at least as safe and effective as unfractionated heparin (UFH) in the initial management of deep vein thrombosis (DVT). However, the effectiveness of using LMWH in the ambulatory management of DVT in a 'real-life' setting has yet to be evaluated. This multicentre retrospective study involving 697 patients considers the outcome data of patients under- going ambulatory DVT treatment with tinzaparin (Innohep(R), Leo Pharmaceuticals, Risborough, Buckinghamshire, UK). During the 6 months following presentation, 17 (2.5%) patients had confirmed thromboembolic complications, of which 14 occurred subsequent to the initial LMWH treatment phase ('late'). There were no deaths in this group. Bleeding complications were reported in 23 (3.4%) patients, with 13 of these being classified as 'late'. Of these, two events were considered major resulting in hospitalization and death. Hospitalization for all causes was 6.8% (45 patients) with 32 patients being admitted for thromboembolic or bleeding complications. Overall mortality was 6.7%. These results compare favourably with published clinical trial data. This study demonstrates that ambulatory treatment of proven DVT with LMWH is both safe and effective.

Heparins and venous thromboembolism: current practice and future directions

Unfractionated heparin (UFH) in adjusted doses and low-molecular-weight heparins (LMWH) in fixed doses are the chosen therapy for the initial treatment of venous thromboembolism. The use of UFH protocols ensures that virtually all patients will promptly achieve the therapeutic range for the activated partial thromboplastin time. However, proper use of UFH requires considerable expertise, can cause inconvenience and has limitations. Unmonitored therapy with subcutaneous LMWH is at least as effective and safe as adjusted-dose UFH, is associated with a considerable reduction of mortality in cancer patients, and permits the treatment of suitable patients in an outpatient setting. LMWH in high prophylactic doses is more effective than UFH and oral anticoagulants for prevention of postoperative venous thrombosis in major orthopedic surgery. Whether thromboprophylaxis should be continued for a few additional weeks after hospital discharge is controversial. LMWH and UFH are equally effective for prevention of postoperative deep-vein thrombosis in cancer patients. In a recent controlled randomized trial, enoxaparin in high prophylactic doses was an effective and safe measure of thromboprophylaxis in ordinary bedridden patients. The efficacy and safety of pentasaccharide (the smallest antithrombin binding sequence of heparin) in the treatment and prevention of venous thromboembolic disorders is currently under investigation.

Low molecular weight heparin therapy for percutaneous coronary intervention: a practice in evolution

Unfractionated heparin (UFH) remains the principal antithrombotic agent during percutaneous coronary intervention (PCI) but is associated with significant limitations including an unpredictable anticoagulation dose response, the requirement for frequent monitoring, and transient rebound hypercoagulability. Low molecular weight heparin (LMWH) represents an attractive alternative due to its predictable dose response relationship, superior antithrombotic efficacy and potential for improved clinical safety, and has been used increasingly in patients with acute coronary syndromes prior to coronary angiography. The rationale and existing data regarding the use of LMWH in PCI is summarized and reviewed. Preliminary clinical guidelines for the use of LMWH in the transition from medical stabilization of patients with acute coronary syndromes to invasive management in the catheterization laboratory are presented.